In a landfill operation, trash and like material is typically spread over a work site in an uncompacted state and then repeatedly traversed by a compaction machine until the material is compressed to a desired degree. Typically, this involves the packing and orientation of solid articles into a more dense and effective arrangement for reducing air voids and like discontinuities. Compaction of material provides increased shear strength and density to enable further use of the material in construction operations.
Compacting operations are largely monitored and controlled intuitively by the machinery operators and supervisors, or by estimating the average characteristics of the material being deposited in the landfill, and then creating a model that tells the operator to compact the material in the landfill based upon that model. Such an approach may tell the operator to “roll” a “layer” a number of times “n” based upon the model. That is, the compactor may be directed to pass over (i.e., “compact”) a worksite surface contour more than one time, as needed, to further compact (i.e., “densify”) the layer of material just added. As such, efforts to electronically provide the operator with detailed information regarding the progress in the compaction effort have been made.
A common method used to determine compaction in landfills is to survey the surface and set stakes. As compacting machines roll the surface, they re-survey the stakes to determine when the practical point of refusal (the point at which diminishing movement causes one to decide that it is no longer cost effective to attempt to drive the surface down more.) has been reached. This method does not yield real time information over the working surface but instead provides a snapshot of progress.
In one known approach, a plurality of target stakes and an electronic unit for transmitting/receiving electronic signals are positioned about a worksite. Using a surveying-like apparatus, the electronic unit is vertically positioned on a tripod and signals are transmitted to and reflected back from the target stakes. The combination of distance and direction measurements is sufficient to determine the location and elevation of the target points, which data can be electronically stored and/or plotted on a map, converted into X-Y-Z coordinates, and used to generate a contour map. Because landfill unloading trucks and a compactor machine must constantly traverse the worksite, the operator must constantly position/reposition the stakes. This is very labor intensive and may generate an inaccurate cross-section. Critically, this cross-section derived contour map may give an indication of volume, but not the density of the landfill layer.
While the recent efforts have advanced the hit or miss approach of the earlier approaches, a simple yet effective method and system for estimating the density of the compacted landfill materials, using conventional apparatus would be desirable.